On May 5, five students at Live Oak High School in Morgan Hill, Calif., were sent home for wearing clothing featuring the American flag. Their offense: trespassing on Mexican heritage during Cinco de Mayo. Administrators called the flag-wearing “incendiary” and likely to cause violence. The school district overrode the decision, and the boys were allowed to return to school. In response yesterday, about 200 students staged a walkout carrying Mexican flags. The question is: Who taught these kids to hate America so much?

There should be nothing disrespectful about the U.S. flag to Americans of Mexican descent or to any other immigrant group. Teaching children that their heritage is at odds with their citizenship promotes disunity and divisiveness. While the high school’s administrators may have been responding to a real public-safety threat, that threat was the product of their failure to instill a sense of national pride in their students.

Identity politics has become such a staple of public life and education in recent decades that incidents like this illustrate the poisonous effects it has on the nation. In the past, immigrant groups would attempt to outdo each other in demonstrating their patriotic attachment to the country that gave them safety, opportunity and freedom. Today, immigrant activist groups think patriotism is at best an inconvenience, at worst a sellout. They have replaced the melting pot with hardening battle lines in a struggle for power.

It is odd that Cinco de Mayo has become a focus of conflict. In Mexico, it is a relatively unimportant, mainly local holiday. But in the United States, it has become the de facto Mexican nationalist day, a far cry from its origins in the 1980s as a marketing gimmick by beer importers to sell brews that taste best with lime wedges.

This is only the latest instance of Old Glory being forced into the closet. In 2006, a Colorado school seeking to placate Mexican nationalists banned the American flag. After a mass student protest, Mexican flags were banned as well. In 2008, Dos Palos, Calif., high school student Jake Shelly was forced to remove a red, white and blue tie-dyed American-flag T-shirt he had worn to school because he was in violation of a dress code banning “shirts/blouses that promote specific races, cultures, or ethnicities.” In 2007, students at Hobbton High School in Sampson County, N.C., were not allowed to wear American-flag-themed clothes on the anniversary of the Sept. 11 attacks because of a general school prohibition on garments featuring flags. The superintendent of schools said that “educators didn’t want to be forced to pick and choose which flags should be permissible.”

Not all flags are created equal. Some flags may be fashion statements, but the American flag is the patriotic symbol of the nation in which we live. This is why the American flag flies outside schools as opposed to, say, Zimbabwe’s. Schools should spend less time telling patriotic students not to cause a ruckus simply by wearing the national colors and more time teaching the kids who are offended by the American flag how wrongheaded their views are. This might require teachers and administrators to begin making value judgments and moral choices for the benefit of the children they are charged with educating. The Stars and Stripes should be a proud statement of unity for all.